What is the relationship between the quality problems of knitted fabric pretreatment and auxiliaries?

The quality of knitted fabric pretreatment (scouring and bleaching) is not only related to the quality of the finished bleached product, but also directly affects the quality of dyeing, printing, and finishing as a semi-finished product. The quality of dyeing and finishing is related to the grey fabric, the equipment and operation, the process technology and execution, the dye, and the auxiliaries.

While producing large quantities of goods, knitted printing and dyeing factories reflect that there are many defects in dyeing and finishing quality. The defects of dyeing and finishing products are an important factor affecting the quality of dyeing and finishing products, and can also show the level of production, management, equipment technology, etc. of dyeing and finishing manufacturers. In production, due to factors such as grey fabrics, semi-finished products, equipment, process level and execution, and dyeing and chemical quality, quality problems may occur. Among them, the selection and use quality of auxiliaries directly affect the quality of dyeing and finishing products. This article mainly discusses the relationship between the generation of common quality problems in knitted fabric pretreatment and the selection of auxiliaries.

The quality of pretreatment (scouring and bleaching) is not only related to the quality of bleached products, but also as a semi-finished product, it directly affects the quality of dyeing, printing, and finishing. Some experts say that 70% of the quality problems of dyeing and finishing products are caused by poor pre-treatment, which makes sense. The quality of dyeing and finishing is related to the grey fabric, the equipment conditions and operation, the process technology and execution, the dye, and the auxiliaries. We focus on the impact of auxiliaries.

1. Poor whiteness and hair effect

Poor whiteness includes impure and uneven whiteness and hair effect that cannot reach 8-10cm/30min or more. This is related to the quality of knitted grey fabric. If the content of low-grade cotton is high, whiteness and hair effect are often not easy to do well. Of course, the most critical issue is process formulation and auxiliaries selection.

In process formulation:

① The amount of H2O2 and NaOH must be sufficient

H2O2: After pretreatment, it not only plays the role of bleaching pigments, but also has the effect of removing impurities (including removing cottonseed hulls). If the amount of H2O2 is insufficient (including decomposition too quickly), whiteness cannot be guaranteed. NaOH not only provides the alkalinity (PH) required for H2O2 bleaching, but also cooperates with the scouring agent to play the greatest role in removing impurities. If the amount of NaOH is insufficient, impurity removal is poor, and the gross effect cannot meet the requirements first, and of course the whiteness cannot meet the requirements either. Therefore, the amount of H2O2 and NaOH can be said to be the primary factor in ensuring whiteness and gross effect.

② Select high-quality scouring agents: The comprehensive effects of scouring agents such as cleaning, emulsification, dispersion, and penetration must be excellent to ensure that impurities are completely removed and whiteness and wool effect are guaranteed. However, the quality of scouring agents on the market is uneven. We must choose products with excellent comprehensive effects instead of just measuring penetration and solid content. Penetration is only one aspect to consider;

③ Oxygen bleaching stabilizers and chelating dispersants: These two additives are mainly used to improve water quality, adsorb and complex metal ions such as Fe3+ in water, and prevent metal ions from catalyzing the rapid and ineffective decomposition of H2O2. If H2O2 decomposes rapidly and ineffectively, its whiteness and wool effect will not meet the requirements, and it will cause brittle damage or even holes in the fabric. Therefore, to achieve whiteness and wool effect, excellent varieties of oxygen bleaching stabilizers should be selected, and the decomposition rate of H2O2 should be considered in the selection. The addition of chelating dispersants can not only chelate iron, etc., but also chelate various impurities in the dispersed water, so that these impurities will not stain the fabric again and cause the whiteness to become dark and gray. Therefore, the chelating dispersant should not only consider its chelating power for metal ions but also its dispersing power;

④ Process conditions: It takes a certain time and temperature for the additives to react with impurities. If the conditions are not met, the pigments and impurities are not completely removed, and the whiteness and wool effect cannot be achieved:

⑤ Washing: Washing after scouring and bleaching is very important. The impurities removed must be cleaned to ensure whiteness and wool effect.

2. Incomplete removal of cottonseed hulls

The removal of cottonseed hulls mainly relies on the expansion and swelling of cottonseed hulls by NaOH under certain conditions, and then the cottonseed hulls are removed by a certain mechanical cleaning force. Incomplete removal is mainly caused by insufficient temperature and time, so sufficient time must be allowed at a certain temperature to completely remove the cottonseed hulls. H2O2 and scouring agents have a certain help in removing cottonseed hulls, so a certain temperature and time must be maintained in the pretreatment to ensure the removal of cottonseed hulls. At the same time, NaHSO3 or anthraquinone substances can be added to help remove cottonseed hulls.

3. Holes and brittleness

In addition to singeing holes, hooking during processing, and original holes in grey cloth, the main reason for holes and brittleness is the presence of metal ions such as Fe3+ and Cu2+ in the H2O2 bleaching bath or on the cloth surface. These metal ions catalyze the decomposition of H2O2 and cause fiber brittleness. If metal ions (such as rust, etc.) are too concentrated in one place, the fibers and yarns will become brittle and form holes. Therefore, high-quality oxygen bleaching stabilizers and chelating dispersants must be selected for H2O2 bleaching to complex and adsorb metal ions on the fabric and in the bleaching bath to prevent H2O2 from decomposing too quickly and causing holes or brittleness. If mercerized recycled alkali is used for bleaching, it must be ensured that the alkali does not contain impurities such as rust. Of course, alkali (not completely removed) or acid (not completely removed) on the fabric surface will also cause brittleness. At the same time, under high temperature and alkali conditions, the fabric will also become brittle in the presence of air. In this case, weak reducing agents such as NaHSO3 can be added to prevent this. In addition, damp and moldy fabrics are also one of the causes of brittleness and holes.